Crustal accretion and dynamic feedback on mantle melting of a ridge centred plume: The Iceland case

A major consequence of the interaction of a plume with an oceanic ridge is the enhanced melt production and associated crust generation. In the case of Iceland crustal thickness as large as 20 to 40 km has been reported. Crustal seismic velocities are high, and have to be explained by thermal or chemical effects. In the first part of the paper we address the question whether extraction of melt out of the plume beneath a slowly spreading ridge and deposition of extracted basalt volumes at the surface produces a dynamic feedback mechanism on mantle melting. To study this question we solve the convection equations for a ridge centred plume with non-Newtonian rheology including melting, melt extraction associated with deposition of cold crust at the surface of the model, and using a simplified approach for compaction. The assumption of cold crust is justified if the thickness of each deposited basaltic layer is less than roughly 1 km. Depending on the buoyancy flux of the plume, crustal thicknesses between 10 and 40 km are modelled, showing characteristic dipping structures resembling the rift-ward dipping basaltic layers of East- and Western Iceland. Comparing the resulting crustal thickness and magma generation rate with models in which the dynamic effect of crust deposition has been suppressed indicates, that melt generation beneath a slowly spreading ridge is considerably damped by the dynamic feedback mechanism if the plume buoyancy flux exceeds 400 to 600 kg/s. Based on the observed crustal thickness of Iceland our models predict a plume buoyancy flux of 1140 kg/s.In the second part we study the accretion of the Icelandic crust by a thermo-mechanical model in more detail based on the Navier–Stokes-, the heat transport and the mass conservation equations including volumetric sources. Hot (1200 °C) molten crustal material is injected into the newly forming crust with a constant rate at different crustal source regions: a) deep, widespread emplacement of dykes and sills including crustal underplating, b) magma chambers at shallow to mid-crustal level, and c) surface extrusions and intrusions in fissure swarms at shallow depth connected to volcanic centres. We identify the material from the different source regions by a marker approach. Varying the relative dominance of these source regions, characteristic crustal structures evolve, showing shallow dipping upper crustal layers with dip angles between 10 and 15°. The thermal structure of the crust varies between cold crust (shallow-source region dominating) and hot crust (deep-source region dominating). We use observations of maximum depth of seismicity to constrain the depth of the 650 °C isotherm and seismological inferences on the lower crust to constrain temperatures in that region. The best agreement with our models is achieved for crust formation dominated by deep dykes and underplating with a considerable influence of magma chamber accretion.     

线性模型的泛最小二乘法

本文首先针对线性模型提出了泛最小二乘法,在设计矩阵不加限制的情形下,得到了参数的泛最小二乘估计量。该方法既发扬了最小二乘法的优点,又克服了它的一些不足,它包含了常见的岭估计和最小二乘估计法;其次讨论了泛最小二乘法的理论依据;接着研究了泛最小二乘估计量的一些统计性质,并与最小二乘估计进行比较,在一定意义上前者优于后者;然后讨论了平衡参数的选取问题;最后,给出一个应用,说明了泛最小二乘法的有效性和可行性。     

Comparison of SARAL and Jason-1/2 altimetry-derived geoids for geophysical exploration over the Indian offshore

Satellite with ARgos and ALtika (SARAL) altimeter includes the ALTIKA payload, a 35.75 GHz Ka band radar altimeter. High pulse repetition frequency of SARAL (4 KHz) satellite provides better along-track information. Jason-1/2 data have been extensively utilized as a follow-up of TOPEX/Poseidon altimeter data for its accurate measurements of the sea surface heights, particularly for geodetic mission of Jason-1. In this study, we have compared SARAL and Jason-1/2 altimetry-derived classical and residual geoids over the Indian offshore using Rapp’s, EGM96 and EGM08 gravity model coefficients, which are of interest for better understanding of geological and structural evolution/interpretation. SARAL and Jason-1/2 data have also been used over the two prominent geological features over the Indian offshore, namely the Bombay High in the western offshore and the 85°E Ridge in the Bay of Bengal. The SARAL altimetry-derived geoids could delineate these major geological/structural features with distinct residual geoidal lows.     

正则化的奇异值分解参数构造法

Tikhonov正则化法引入正则化参数和稳定泛函来改善矩阵的病态性。稳定泛函表示为参数的二范约束时,正则化矩阵为单位阵的正则化法即为岭估计法。通过对岭估计的方差与偏差进行分析可知,岭估计改善矩阵病态性的同时也过度地引入了偏差,降低了解的可靠性,对较大奇异值的修正不能有效地减小估计的方差,却引入了偏差,而对较小奇异值的修正可有效地减小估计的方差。因此,选择较小奇异值特征向量构造正则化矩阵,调节各奇异值的修正,可有效减小参数估计的方差,减少偏差的引入,得到更为可靠的参数估计。通过试验证明了该方法的有效性。     

总体最小二乘用于线阵卫星遥感影像光束法平差解算

顾及像点观测方程的系数矩阵中存在随机误差,提出了基于总体最小二乘的线阵卫星遥感影像光束法平差模型。在假定像点观测误差和系数矩阵误差均为独立、等精度分布的基础上,利用拉格朗日条件极值法推导了包含外方位元素虚拟观测方程和控制点误差方程的总体最小二乘光束法平差算法的具体公式和计算方法。该方法利用方差分量估计确定各类虚拟观测值的方差,可求解包含多类虚拟观测量的平差问题,并可用先验信息或岭迹法确定系数矩阵观测值的权比例系数,从而克服了现有总体最小二乘虚拟观测方法不能处理多类虚拟观测值的不足,确保了光束法平差可正确有效求解。分别利用模拟算例与两组真实影像进行了试验验证。结果表明,相比于常规最小二乘虚拟观测法以及现有总体最小二乘虚拟观测方法,本文方法具有更高的求解精度与适应性。相较于传统线阵卫星遥感影像光束法平差方法,本文方法可以获得更高的平差计算精度。     

陕西秦岭元古宇松树沟岩组变质火山岩的地球化学特征及地质意义

中新元古界松树沟岩组出露于周至黑河黄草坡南及榨水丰河街北等地,为一套呈残块分布的含气孔、杏仁,局部具枕状构造,角闪岩相变质的中基性火山岩系夹少量碎屑岩。通过对该岩组的分析,其与洋中脊岩石化学特征较为相似,曲线较为平坦,轻稀土元素相对富集、重稀土元素相对亏损。微量元素蛛网图显示高场强元素及大离子亲石元素富集的特征。从构造环境进行分析,松树沟岩组形成于洋中脊环境。     

Visitors' awareness of ICZM and WTP for beach preservation in four European Mediterranean regions

This paper discusses the results of a multi-country survey about private stakeholders' contribution to coastal preservation. It was conducted in four coastal sites of Greece, Italy and France, in order to collect information about beach visitors' perception of Integrated Coastal Zone Management (ICZM) and their willingness to pay (WTP) for beach preservation, intended here as defence from erosion. In order to find out whether ICZM perception is a determinant of WTP, regression analysis is applied. Results show that in these sites respondents have a low level of information about the nature of ICZM, despite local authorities having implemented some ICZM strategies for preserving the coast. Nevertheless, those who are informed about ICZM have a higher probability of paying for beach preservation. This suggests to policymakers that promoting public awareness about ICZM may increase the probability of paying. Finally, some categories of visitors, such as women and young and middle-aged people, have a higher probability of paying than men and older people, thus suggesting a more sensitive attitude to beach preservation. Therefore, policy-makers should also pay attention to the categories of visitors less likely to pay.     

青岛市灵山湾海水浴场表层沉积物粒度冬季变化特征及其原因

于2013年11月、2014年1月及3月在青岛市灵山湾海水浴场进行了3次表层沉积物采样,对粒度组分和粒度参数平面分布的变化进行了分析。结果表明,本区沉积物整体有变粗的趋势,细砂组分特别是极细砂和粉砂组分含量下降明显,分选性变好,正偏态及高峰度分布区扩大,粒度参数高值分布区被消除。粒径趋势分析表明,在涨潮流与强盛的冬季风驱动的风浪、沿岸流的综合作用下,研究区沉积物总体呈北东-南西向沿岸输运,运移趋势变化受到波浪、潮流水动力条件与地形相互作用的影响。短期的波能变化足以改变沙滩地貌,从而影响表层沉积物的分布。可为浴场维护提供理论依据。     

Coastal erosion in Shandong of China: status and protection challenges

Shandong has more than 70% of natural coasts are under erosion. Coastal erosion started from the 1970’s and became a very serious problem at 1990’s. The dramatic decrease of sediment supplies from rivers caused rapid erosion at the delta and estuary areas, especially in the abandoned Yellow River Delta. Most sandy coasts along the Peninsula were eroded due to lack of sand supply and interruption of alongshore sediment drift, sand dredging from the beach or the offshore area caused serious erosion during short time. Sea-level rise causes slow but constant shoreline retreats and became a more serious threat. Different types of hard solutions for coastal protection against erosion were used in Shandong. Seawalls are most widely used, especially at the Yellow River Delta and city center waterfront. Groynes, jetties and breakwater are used on the north and east sandy coast of the Peninsula. Hard approaches are effective to protect the coast erosion but not change the erosion causes and led secondary impact on the coast. Soft engineering solution or the combined solutions are taken into acts. Beach nourishment is mostly considered as the better soft solution, especially to those tourists attracting sandy beaches along the Shandong coast. Long term monitoring and continuous lessons learning from the coastal erosion management will be adaptive for better coast solution in the future.     

2011年6月7—8日平顶山地区高温天气过程的诊断分析

2011年6月7—8日平顶山市大部分地区出现了40℃以上的高温天气,尤其是8日平顶山地区7个站的自动观测站的最高气温都在40℃以上。利用NCEP再分析资料和常规观测资料对这次极端高温天气进行了分析,结果表明：这次高温天气过程的主要影响系统为700hPa上的暖脊和地面的暖低压,7—8日平顶山地区天空晴朗,辐射升温对高温天气的出现比较有利;物理量的诊断分析表明,出现高温天气时平顶山地区上空空气干燥并且有强烈的下沉运动和明显的暖平流,下沉增温和平流增温有利于高温天气的出现。